1. Field of the Invention
The invention relates to a pressure sensor for a motor vehicle having a sensor element arranged in a sensor housing, a base connected with the sensor housing, a pressure space defined by the base and a diaphragm which is held via a sealed connection to the base, a pressure bore extending through base to the pressure pressure space, and an actuating element arranged on a side of the diaphragm facing away from the pressure space for non-contact actuation of the sensor element.
2. Description of the Related Art
Pressure sensors having diaphragms with actuators arranged thereon on a side facing away from a pressure space are used in technology for various tasks and are generally known. Where such pressure sensors are concerned, it is often important to prevent leaks, even after lengthy use. This prevention of leaks is required when the medium acting upon the pressure sensor is a medium such as, for example, hydraulic fluid that is harmful to the immediate surroundings of the pressure sensor or to the environment or when the medium is a flammable medium such as, for example, fuel. In a motor vehicle, the escape of fuel from a pressure sensor increases the risk of fire. Even if the the medium is not harmful or flammable, the medium escaping from pressure sensors may damage control devices or make them temporarily inoperative. The diaphragm is a critical component in terms of leakage, because the diaphragm may break as a result of frequent actuation or even due to a material fault, thus resulting in a sudden serious leak.
To avoid the risk of medium escaping from a pressure sensor, the pressure sensor could be provided with cladding, in a similar way to the double-walled cladding of oil tanks to be installed in the ground. Such cladding is costly and not entirely reliable, however, because electrical leads would have to be led sealingly out of it and the cladding would also have to be sealed off relative to the base of the pressure sensor.
It is an object of the present invention to design a pressure sensor having an actuator mounted on a diaphragm such that the pressure sensor is protected against leakage in a cost-effective and reliable manner.
According to an embodiment of the present invention, the object is met by a pressure sensor having a diaphragm and an actuating element that are surrounded by a sealing cap connected sealingly to the base of the pressure sensor housing.
In the sensor according to the present invention, the sealing cap defines a further pressuretight shutoff of the pressure space arranged behind the diaphragm. Since this further shutoff of the pressure space is only required to surround the pressure space and the actuating element, the further shutoff of the pressure space can be made relatively small, so that it does not appreciably increase either the costs of the pressure sensor or its construction volume.
The sealing cap may be designed in the form of a hat with a flange which faces one side of the diaphragm with a clearance therebetween such that the flange limits the maximum flexion of the diaphragm. The sealing connection of the sealing cap is made to the base. A middle region of the sealing cap has a cylinder leading over the actuating element. This configuration of the sealing cap has a double function. The first function is to ensure the prevention of leaks in the event of a failure of the diaphragm and the second function is to limit the maximum bulge of the diaphragm under high pressure. Accordingly, the sealing cap prevents overstretching and breaking of the diaphragm even during the occurrence of pressure peaks.
For use in hydraulic systems and, in general, in a motor vehicle, the actuating element of the pressure sensor may be a magnet and the sensor element a Hall effect device and the sealing cap may consist of a nonmagnetic material. In principle, however, the flexion of the diaphragm may also be measured in another non-contact way such as, for example inductively or capacitively.
The diaphragm and the sealing cap may be made from high-grade steel so that the pressure sensor may be cost-effectively produced and so that the pressure sensor can withstand even aggressive media without the risk of corrosion.
The sealing cap may be connected via a sealed connection to the diaphragm and the base particularly cost-effectively when the sealing cap is connected to the diaphragm and the base by welding.